The present invention relates to instruments for measuring acceleration, more exactly to compensation accelerometers in which a movable sensitive member that reacts to acceleration is held in a neutral position by a negative feedback system.
An accelerometer is known from prior art (see, e.g., U.S. Pat. No. 3,702,073), which comprises a body with a sensitive member arranged therein and with two magnetic systems of a magnetoelectric torquer. The pendulous unit of the accelerometer is made of a single plate of melted quartz and comprises a movable portion made in the form of a vane and connected to a supporting flame that is stationary, by means of two flexible tapered plane-parallel connectors. Each side of the vane has a metal coating, forming a capacitor with the inner surface of the magnetic system on each side of the vane. The clearance of a capacitance pick-off (it is also the clearance of a gas damper) is farmed by means of three protrusions of equal height which are made on the two sides of the supporting frame.
It is known that the use of monocrystalline silicon, without impairing the accuracy of measurement of the characteristics of an accelerometer, provides a substantial technological advantage, reducing the labor input, and consequently, the cost of the accelerometer.
The main drawback of the accelerometer under consideration is that it is not possible to use therein monocrystalline silicon instead of melted quartz as the material of the pendulous unit. However, it is not possible to use a silicon pendulous unit in this construction, since silicon is not an insulator and requires oxidation in order to create an insulation layer. Since it is not possible to achieve a substantial thickness of the insulation layer by oxidation, there will be large capacitances between the electrodes made on the oxidated surface of the silicon and the body of the pendulous unit, these capacitances shunting the working capacitances of the pick off and not making it possible to ensure the normal functioning of the accelerometer.
The instrument disclosed in USSR Inventor""s Certificate No. 1679395 is the analog most similar to the proposed accelerometer.
This accelerometer also comprises a body, a sensitive member and two magnetic systems of a magnetoelectric torquer. The pendulous unit has a vane, a support frame with protrusions and two flexible plane-parallel connectors. All of these elements are made of a unitary plate of monocrystalline silicon.
The vane of the pendulous unit is a movable electrode of a differential pick off, while the stationary electrodes are made on intermediate insulating rings. The intermediate insulating rings are arranged between the pendulous unit and the face surfaces of the magnetic systems of the magnetoelectric torquer.
This construction makes it possible to use a silicon pendulous unit.
However, the arrangement of the insulating rings between the pendulous unit and the magnetic systems of the torquer leads to an increase in the dimensions of the accelerometer in the direction of its axis of sensitivity, and also to a reduction of its reliability because of the necessity of removing coils secured on the vane to substantial distances from the center of gravity of the pendulum.
Furthermore, the traditional arrangement of the flexures in the pendulous unit does not make it possible to reduce the dimensions of the accelerometer in the direction perpendicular to the axis of sensitivity of the accelerometer.
Means for protection against impact action are not provided in the directions perpendicular to the axis of sensitivity of the accelerometer.
The object at the base of the instant invention is the creation of a compensation pendulous accelerometer which has increased accuracy of the measurement of an acceleration vector, while maintaining or reducing the size and enhancing the vibration resistance.
The stated object is achieved in a compensation pendulous accelerometer comprising a body in which a pendulous unit is positioned that is made of a unitary plate of a silicon monocrystal and comprises a movable vane on a flexible suspension and a support frame with protrusions on both sides of the support frame for positioning, two electrical insulation means which are secured on the two sides oil the support frame on the protrusions, and two magnetic systems, each of which comprises a core, a permanent magnet and a pole piece, and is secured on a corresponding electrical insulation means, two coils of a torquer with leads, each coil of which is positioned in a clearance of a corresponding core and is secured on a corresponding side of the movable vane, in that in accordance with the invention, the flexible suspension comprises at least two flexible members arranged at an angle of 90 degrees relative to one another symmetrically relative to an axis of symmetry of the pendulous unit, wherein each electrical insulation means is made in the form of a bush that encompasses the core of a magnetic system along the outer side surface, and the support frame of the pendulous unit with its protrusions positioned on both sides abuts against the faces of the bushes, forming common planes with core faces facing the pendulous unit, wherein the accelerometer additionally comprises a means for fixing the magnetic systems relative to the pendulous unit, this means being placed on the pendulous unit and each electrical insulation means.
It is advisable that the accelerometer comprises a mounting means secured in the body and serving to fix the pendulous unit relative to the body, wherein one of the electrical insulation means is rigidly connected to the mounting means.
It is useful that the means for fixing the magnetic systems relative to the pendulous unit comprise a holding bush, an inner cylindrical surface of which contacts with an outer cylindrical surface of each of the electrical insulation means, and a support ring, an outer cylindrical surface of which contacts with an inner cylindrical surface of the holding bush, wherein the electrical insulation means and the pendulous unit would be compressed between a collar, made on the inner cylindrical surface of the holding bush, and the support ring, and two rings secured on the two sides of the support frame coaxially with the coils, each of the rings would encompass a corresponding insulating bush, wherein one of the rings would be mounted on a corresponding bush without a clearance and the second ring would be secured on a corresponding bush with a clearance.
It is also useful that the holding bush and the support ring be made of electrically conducting material, wherein the accelerometer would comprise two insulating plates with metallized surfaces on one side, wherein each insulating plate is secured with the insulating side on the outer face surface of a corresponding core, and the metallized surfaces be electrically connected to the holding bush and the support ring to form an electrostatic screen.
It is advantageous that the tip of the 90xc2x0 angle between the two flexible members be located on the vane.
It is useful that that the tip of the 90xc2x0 angle between the two flexible members be located on the support frame.
It is advisable that the accelerometer comprises two additional flexible members, wherein the four flexible members of the flexible suspension form a square.
It is useful that a slot for removing the mechanical stresses in the flexible suspension be made in the support frame, to the right or left of the axis of symmetry of the pendulous unit on the section between the securing of the flexible suspension and the closest protrusions.
It is advantageous that both rings be made of material selected from the group consisting of silicon, quartz, glass, sitall and a material, the coefficient of thermal expansion of which is close to the coefficient of thermal expansion of silicon.
It is also advisable that the coils be secured on the vane by means of two transition washers with a central cylindrical hole, and the pole pieces of the magnetic systems have central cylindrical protrusions facing the pendulous unit and entering the central holes of the transition washers with a clearance, wherein the clearance between the cylindrical surface of one of the protrusions and the cylindrical surface of the central hole of a corresponding transition washer be made much less than the clearance between the coils and the magnetic systems.
It is useful that the transition washers for securing the coils of the torquer be made of insulating material and have contact terminals for connecting the leads of the coils of the torquer.